1. Field of the Invention
The present invention relates to a method of discriminating the quality of die-cast articles, a method of stratifying die-cast articles by quality, and a die-casting process utilizing the method.
2. Description of the Related Art
In the casting field, a higher quality of cast articles are required and it is desired that individual articles are nondefective.
In conventional die-casting, phenomena occurring during the casting process are not completely understood and casting defects cannot be detected within the stage of casting.
Japanese Unexamined Patent Publication (Kokai) No. 63-72467 disclosed a process in which a pressure sensor and a temperature sensor are disposed on a die and measured values therefrom are compared with a preset reference value to control the casting condition.
The above-mentioned conventional process, however, has drawbacks in that it cannot discriminate the product quality in terms of an inclusion of broken chilled layer and a gas inclusion, which exert a great influence upon the quality of a die-cast article, and in that a shrinkage cavity defect cannot be strictly discriminated because of lack of a proper reference value.
In the pressure die-casting process, a molten metal is introduced into a die cavity of a die through an injecting port of the die, the introduced molten metal is primary-pressurized in the die cavity with a pressure through the injecting port and then additionally secondary-pressurized in the die cavity with a pressure through a pressurizing port other than the injecting port, to provide a cast article having a high density.
Japanese Examined Patent Publication (Kokoku) No. 59-13942 discloses a die-casting apparatus having an improved constitution of the pressurization mechanism to ensure the pressurization effect and satisfy the requirement for a high quality die cast article.
With the conventional apparatus, however, the pressurization effect varies when the casting conditions vary, with the result that a shrinkage cavity occurs and the allowance for machining fluctuates at the portion directly subjected to the pressure upon pressurization.